Computing devices, such as notebook computers, Personal Data Assistants (PDAs) and mobile handsets have user interfaces which are referred to as Human Interface Devices (HID). A touch sensor pad is one type of human interface device that is widely used in these type of devices. A basic notebook touch sensor pad emulates the function of a personal computer mouse. A touch sensor pad is typically embedded within a PC notebook to provide built in portability. A touch sensor pad replicates a mouse's XY movements by using two defined axes which contain a collection of sensor elements that detect the position of a conductive object, such as a finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touch pad, or by tapping commands on the touch sensor pad. The touch sensor pad provides a user interface device for performing such functions as positioning a cursor, or selecting an item on a display. These touch sensor pads can include multi-dimensional sensor arrays or slider arrays. The sensor array may be one dimensional, detecting movement in one axis. The sensor array may also be two dimensional detecting movements within two axes.
Within a capacitive sensor array there is needed the ability to detect differences within the capacitance of a capacitive switch responsive to the placement of a user's finger upon the capacitive switch. In addition to detecting the placement of a finger upon a capacitive switch and the associated change in capacitance caused by the finger, there is the need to make the sensing circuitry resistant to external interferences within the capacitive sensor array. Examples of external interferences include cell phones whose transmissions may cause inadvertent detections of increases of capacitance upon the switch. Additionally, electrical main circuits such as those associated with air conditioning or other high use electrical energy units can cause interference within capacitive sensor arrays. Other types of interferences and inaccuracies within the capacitive sensing circuitries may also lend themselves to errors in detection of particular capacitance values within capacitive sense array circuitry. Thus, there is a need for providing a capacitive touch sensor circuitry that enables the detection of a finger upon a capacitive sense array while limiting the amount of detections based upon external interferences and inaccuracies and interferences inherent within the detection circuitries.